Amine-based solvent solutions are commonly used for absorption of carbon dioxide (CO2) from low-pressure flue gas streams produced as a consequence of industrial combustion processes. Examples of effective amines commonly used include monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA). However, while amines are effective for CO2 capture and removal from gas streams, they are degraded and lose their efficacy by irreversible reactions with flue gas impurities (e.g. O2, SO2, and CO). Consequently, the degraded amines need to be continually replaced to maintain efficient CO2 capture and removal, resulting in increased costs to operate and manage industrial combustion processes. The flue gas impurities may also react with various amines to form heat-stable salts (HSS). The HSS species are corrosive and are typically generated by reactions of amines with oxidizing agents to form short-chain carboxylic acids. These acids subsequently quickly bond with amines to form stable salts. Not only do HSS have no capacity to absorb CO2, their presence in solvent solutions make it difficult to regenerate the solvents, at least under typical processing conditions used to regenerate and recycle amine solvent solutions used in CO2-capture systems.
Some conventional amine-based solvent solutions regenerating systems use distillation to separate the amines from the HSS contaminants. Since distillation is achieved based on boiling point differences, a large energy input is required to separate the amines and water from the HSS. This makes distillation a very energy-demanding process, which gives rise to high operating costs. In addition, co-evaporation commonly occurs since various HSS and degradation products may have boiling points close to those of the amines. As a result, the amine solvent solutions may still be contaminated by HSS after distillation.